"Sadly, because of cutbacks it's hard to retain good staff and the resident meals suffer, because no one really cares," she said.

Families and aged care workers say they are concerned about a drop in quality of food in nursing homes.

The amount spent on food in aged care facilities has dropped to just over $6 a day — $2 less than the sum spent on prison inmates.

Other meals photographed completely unidentifiable blobs. These were "texture-modified meals", for people who have difficulty swallowing, the ABC reported.

"My mother has dementia but still knows she is fed up with this meal and doesn't like it," one daughter told the broadcaster.

While some of the meals looked healthy and nutritious, the opposite was often the case.

Dietitian Cherie Hugo, who looked at more than 800 Australian aged care facilities, found they were spending an average of just $6.08 a day on food per resident.

That's $2 less than is spent on prison inmates and far less than other adults spend, with the average Australian eating $17-worth of food per day.

Dr Hugo told the program one of her biggest concerns was that the amount spent on aged care food had dropped by 31 cents per person per day in a year, while the figure spent on supplements had risen by 50 cents.

Health Services Union national secretary Gerard Hayes called it a "disgrace".

The shocking findings come after Prime Minister Scott Morrison announced a royal commission into the aged care sector on Sunday following what he called an "alarming and disturbing" spike in elder abuse and poor standards.

Four Corners also uncovered horrifying abuse allegations, including one elderly resident who said she was left in bed for three hours, mostly in darkness.

Blind and partially deaf Catherine Logan was seen breaking down in tears to her granddaughter after she was left alone by staff, with her relative having to empty the full commode left by her bed.

"In her world, it was black," said her granddaughter Dayna Vereguth. "She couldn't hear and she could smell that there was faeces next to her and she knew she had to press a button, of which she was scared to do, because she didn't know the response that she would get from the staff member."

Nurse Katrina Legzdin told the program: "Some people get really depressed and you have a resident saying, 'Can you give me a pill to kill me?' They just want to die and you don't have five minutes to spend sitting there with them."

The Government has fended off claims by Labor that it has cut aged care funding, with Mr Morrison telling Parliament it has spent more than $1 billion extra on the sector annually.

He said yesterday the royal commission would look at looming issues in the sector, including the quality of residential and home aged care.

It will also examine how young Australians with disabilities are cared for in such facilities, and why thousands of young people are living in nursing homes.

Elderly Australians are staying in their own homes for longer than ever, to have more time with their families - but when they do move into residential care, they can arrive with serious problems such as advanced dementia, Mr Morrison warned.

"They are coming into aged care when their needs are more acute," he told news.com.au. "And that's a fairly big gear change from where residential aged care has been, and had demands placed on it, in the past."

Those who stay at home for as long as possible are more expensive and difficult to care for than younger residents.

"There used to be more of a softer entry into residential aged care with the acuteness of people's needs," the Prime Minister said. "That now has sharpened up a lot. And so when people are coming in, they are adding a much higher level of care."

Mr Morrison said there was also "a sociocultural demographic bubble coming through on the make-up of the population".

It is creating a fresh burden for facilities looking after immigrant Australians, who often lose their English and revert to the languages they were born with as they age.

"You are seeing more Australians from different ethnic backgrounds coming into the aged care sector than you've ever seen before," Mr Morrison said.

"When you are suffering from dementia, often you revert back to your childhood.

"You've spoken English your entire working life in Australia and all of a sudden you've gone back to speaking Greek, or Italian, or Arabic, or Chinese, whether it's Mandarin or Cantonese, whichever.

"And so the system has to deal with that too."

Watch Part One of the investigation into aged care on Four Corners on ABC iview. Part Two airs on September 24.